It is always worth appealing, provided you do it properly. Don’t forget, it’s not a ‘fine’ it’s an invoice. There is plenty of advice out there on what to do, the golden rule though is that you NEVER tell them who was driving the car.
Since airport bylaws apply, the keeper cannot be held liable and you, as the registered keeper, are under no obligation to tell them who was driving.
As it’s APCOA as well, it’ll be a piece of piss, as long as you follow the guidance. Moneysaving expert has a huge amount of advice as does this one
https://www.ftla.uk/index.php
I’ve never paid a ‘fine’ and I’ve had them from both train stations and airports!
Last bit, I forgot to pay the Dart Charge when crossing the Thames and got a letter advising, because it was a first offence, I had 2 weeks to pay the original £2.50 charge, which seems like a much better way to go about things and I’ll definitely be paying next time I cross…